Enhancing the coherent-state lifetime of a Kerr-cat qubit through leakage suppression (Part I)

A Kerr-nonlinear resonator subject to a two-photon drive stabilizes opposite-phase coherent states and their quantum superpositions via Hamiltonian confinement [1]. These states encode a Kerr-cat qubit, whose Bloch-sphere has one protected axis due to the large phase-space separation of the coherent states. The Kerr-cat qubit is therefore expected to exhibit strong noise bias, making it a useful component for higher-order quantum-error-correction codes. However, it was experimentally observed that spurious processes can promote the population of the Kerr-cat qubit to higher excited states, corresponding to leakage outside of the computational manifold. This effect is suspected to severely impact the lifetime of coherent states and overall qubit performance [2].

In this two-part talk, we will show experimental results demonstrating an enhancement in coherent-state lifetime by suppressing leakage out of the ground-state manifold. We will explain our strategies to limit the exposure to leakage-inducing noise sources, and introduce dissipation that selectively targets transitions between excited states and the Kerr-cat qubit computational manifold.

This is part one of a two-part talk.

[1] Grimm, A., Frattini, N. E. et al. Nature 584, 205-209 (2020)

[2] Frattini, N. E., Cortiñas, R. G. et al. Phys. Rev. X 14, 031040 (2024)